Mechanisms of Response essays

Mechanisms of Response essays The human body is built with its own immunity system. It provides defenses against foreign objects in the body and prevents disease. Specific diseases have a specific reaction- the immune system has a mechanism of response for each particular foreign substances. A foreign molecule that draws specific response lymphocytes is called an antigen; antigens are the molecules that are rejected by the body. Antigens are inclusive of molecules that belong to viruses, bacteria, fungi, protozoa, and parasitic worms. However, antigenic molecules can also be found on the surfaces of foreign materials such as pollen and transplanted tissue (as in the situation of a skin graft.) A skin graft is a patch of skin that is surgically removed from one part of the body and transplanted to another. It replaces tissue that has been destroyed or creates new tissue where none exists. One way that an antigen begins an immune response is by activating B cells to secrete proteins called antibodies. The term antigen is a contraction of anti-body-generator. Each antigen has a particular molecular shape and stimulates certain B cells to secrete antibodies that interact specifically with it. In fact, B and T lymphocytes even distinguish among antigens with molecular shape s that are only slightly different. So, in contrast to the nonspecific defenses, the immune system targets specific invaders. B cells and T cells can recognize specific antigens by their plasma membrane-bound antigen receptors. On B cells, these are actually transmembrane versions of antibody molecules and are often referred to as membrane antibodies. The antigen receptors on a T cell, called T cell receptors, are structurally related to membrane antibodies, and they recognize antigens just as specifically; contrary to antibodies, T cell receptors are never produced in a secreted form. Just one T or B cell can hold about 100,000 receptors for antigen, all with exactly the same specificity...